Annelids

The annelids (also called "ringed worms"), formally called Annelida (from Latin anellus "little ring"), are a large phylum of segmented worms, with over 17,000 modern species includingragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments. The basic units of the annelid excretory system are either protonephridia, which have tubules (solenocytes) that end blindly within cells, contain flagella (whiplike projections), and are joined to a common duct that drains to the outside; or metanephridia, which are funnel-shaped structures containing cilia (short, hairlike processes) that open to the outside.Nephridia are organs of excretion in the annelids. Flood your worm with water. Observe the body wall under a dissecting microscope. The nephridia are coiled tubules with an expanded funnel-shaped nephrostome. The nephrostome is attached to the septum dividing two segments and opens into the anterior segment. The tubule opens to the outside through the body wall within the posterior segment. Filtration of the blood across the tubule wall can occur because of the close association between capillaries and the nephridium.

Lumbricus-terrestris, Common earth worm

Lumbricus terrestris is a large, reddish worm native to Europe, but now also widely distributed elsewhere around the world (along with several other lumbricids) due to human introductions. In some areas where it has been introduced, some people consider it to be a serious pest species since it is outcompeting native worms.

Lamellibrachian-Tube wormsTube worms have no gut and gain nutrients from chemoautotrophicbacteria living inside them.In annelids the points at which fluid enters the protonephridia or metanephridia are on the forward side of a septum while the second-stage filter and the nephridiopore (exit opening in the body wall) are in the following segment. As a result the hindmost segment (before the growth zone and pygidium) has no structure that extracts its wastes, as there is no following segment to filter and discharge them, while the first segment contains an extraction structure that passes wastes to the second, but does not contain the structures that re-filter and discharge urine.

Hirudo-medicinalis

Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways. For example, leeches do not have bristles and the external segmentation of their bodies does not correspond with the internal segmentation of their organs. Their bodies are much more solid as the spaces in their coelom are dense with connective tissues. They also have two suckers, one at each end.